Cutting tool

ABSTRACT

A cutting tool comprises a substrate and a coating layer provided on the substrate, the coating layer including a multilayer structure layer composed of a first unit layer and a second unit layer, and a lone layer, the lone layer including cubic TizAl1-zN crystal grains, an atomic ratio z of Ti in the TizAl1-zN being 0.55 or more and 0.7 or less, the lone layer having a thickness with an average value of 2.5 nm or more and 10 nm or less, the multilayer structure layer having a thickness with an average value of 10 nm or more and 45 nm or less, one multilayer structure layer and one lone layer forming a repetitive unit having a thickness with an average value of 20 nm to 50 nm, a maximum value of 40 nm to 60 nm, and a minimum value of 10 nm to 30 nm.

TECHNICAL FIELD

The present disclosure relates to a cutting tool. The presentapplication claims priority based on Japanese Patent Application No.2019-186821 filed on Oct. 10, 2019. The disclosure in the Japanesepatent application is entirely incorporated herein by reference.

BACKGROUND ART

Conventionally, cutting tools made of cemented carbide or cubic boronnitride (cBN) sintered material have been used to cut steel, castings,and the like. When such a cutting tool is used to cut a workpiece thecutting tool has its cutting edge exposed to a severe environment suchas high temperature and high stress, which invites wearing and chippingof the cutting edge.

Accordingly, suppression of wearing and chipping of the cutting edge isimportant in improving the cutting performance of the cutting tool andhence extending the life of the cutting tool.

For the purpose of improving a cutting tool's cutting performance (e.g.,breaking resistance, wear resistance, impact resistance, and oxidationresistance), development of a coating for coating a surface of asubstrate of cemented carbide, cBN sintered material and the like isunderway. Inter alia, a coating including a layer composed of a compoundof aluminum (Al), titanium (Ti), and nitrogen (N) (hereinafter alsoreferred to as “AlTiN”) can have high hardness and also enhanceoxidation resistance (for example, see Japanese Patent Laid-Open No.2016-137549 (PTL 1), Japanese Patent Laid-Open No. 2017-185609 (PTL 2),Japanese Patent Laid-Open No. 2017-189848 (PTL 3), and Japanese PatentLaid-Open No. 2019-063982 (PTL 4)).

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laid-open No. 2016-137549

PTL 2: Japanese Patent Laid-Open No. 2017-185609

PTL 3: Japanese Patent Laid-Open No. 2017-189848

PTL 4: Japanese Patent Laid-open No. 2019-063982

SUMMARY OF INVENTION

The presently disclosed cutting tool is

a cutting tool comprising a substrate and a coating layer provided onthe substrate,

the coating layer including a multilayer structure layer composed of afirst unit layer and a second unit layer, and a lone layer,

the first unit layer and the second unit layer being alternatelystacked,

the multilayer structure layer and the lone layer being stacked suchthat more than one multilayer structure layer and more than one lonelayer are alternately stacked,

the first unit layer including cubic Al_(x)Ti_(1-x)N crystal grains,

the second unit layer including cubic Al_(y)Ti_(1-y)N crystal grains,

the lone layer including cubic Ti_(z)Al_(1-z)N crystal grains,

an atomic ratio x of Al in the Al_(x)Ti_(1-x)N being 0.8 or more and0.95 or less,

an atomic ratio y of Al in the Al_(y)Ti_(1-y)N being 0.7 or more andless than 0.8,

an atomic ratio z of Ti in the Ti_(z)Al_(1-z)N being 0.55 or more and0.7 or less,

the first unit layer having a thickness with an average value of 2.5 nmor more and 5 nm or less,

the second unit layer having a thickness with an average value of 2.5 nmor more and 5 nm or less,

the multilayer structure layer having a thickness with an average valueof 10 nm or more and 45 nm or less,

the lone layer having a thickness with an average value of 2.5 nm ormore and 10 nm or less,

one multilayer structure layer and one lone layer forming a repetitiveunit having a thickness with an average value of 20 nm or more and 50 nmor less, a maximum value of 40 nm or more and 60 nm or less, and aminimum value of 10 nm or more and 30 nm or less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of one embodiment of a cutting tool by wayof example.

FIG. 2 is a schematic cross section of one embodiment of the cuttingtool by way of example.

FIG. 3 is a schematic cross section of another embodiment of the cuttingtool by way of example.

FIG. 4 is a schematic cross section of a CVD apparatus used formanufacturing the cutting tool according to the present embodiment.

FIG. 5 is a schematic cross section of a gas introduction pipe of theCVD apparatus used in manufacturing the cutting tool according to thepresent embodiment.

DETAILED DESCRIPTION Problem to be Solved by the Present Disclosure

PTL 1 to PTL 4 describe that the layer of AlTiN configuring the coatingforms an ultra-multilayer structure to improve the cutting performanceof the cutting tool provided with the coating. In recent years, however,more efficient (or higher feed rate) cutting has been demanded, andfurther improvement is expected in thermal cracking resistance and wearresistance of a cutting tool used for high speed processing ofspheroidal graphite cast iron (e.g., FCD600), in particular.

The present disclosure has been made in view of the above circumstances,and an object thereof is to provide a cutting tool having excellentthermal cracking resistance and excellent wear resistance.

Advantageous Effect of the Present Disclosure

According to the present disclosure, a cutting tool having excellentthermal cracking resistance and excellent wear resistance can beprovided.

Description of Embodiments of the Present Disclosure

Initially, embodiments of the present disclosure will be listed anddescribed.

[1] A surface-coated cutting tool according to the present disclosure is

a cutting tool comprising a substrate and a coating layer provided onthe substrate,

the coating layer including a multilayer structure layer composed of afirst unit layer and a second unit layer, and a lone layer,

the first unit layer and the second unit layer being alternatelystacked, the multilayer structure layer and the lone layer being stackedsuch that more than one multilayer structure layer and more than onelone layer are alternately stacked,

the first unit layer including cubic crystal grains,

the second unit layer including cubic Al_(y)Ti_(1-y)N crystal grains,

the lone layer including cubic Ti_(z)Al_(1-z)N crystal grains,

an atomic ratio x of Al in the Al_(x)Ti_(1-x)N being 0.8 or more and0.95 or less,

an atomic ratio y of Al in the Al_(y)Ti_(1-y)N being 0.7 or more andless than 0.8,

an atomic ratio z of Ti in the Ti_(z)Al_(1-z)N being 0.55 or more and0.7 or less,

the first unit layer having a thickness with an average value of 2.5 nmor more and 5 nm or less,

the second unit layer having a thickness with an average value of 2.5 nmor more and 5 nm or less,

the multilayer structure layer having a thickness with an average valueof 10 nm or more and 45 nm or less,

the lone layer having a thickness with an average value of 2.5 nm ormore and 10 nm or less,

one multilayer structure layer and one lone layer forming a repetitiveunit having a thickness with an average value of 20 nm or more and 50 nmor less, a maximum value of 40 nm or more and 60 nm or less, and aminimum value of 10 nm or more and 30 nm or less.

The above cutting tool thus configured has excellent thermal crackingresistance and excellent wear resistance. As used herein, “thermalcracking resistance” means resistance to cracking of a cutting edgeportion in a cutting process in which the cutting edge portion attainshigh temperature. As used herein, “wear resistance” means resistance towear at a flank face.

[2] The lone layer preferably has a thickness with an average value of2.5 nm or more and 5 nm or less. By defining in this way, the cuttingtool can be further excellent in thermal cracking resistance.

[3] Preferably, the repetitive unit has a thickness with an averagevalue of 25 nm or more and 50 nm or less, a maximum value of 50 nm ormore and 60 nm or less, and a minimum value of 12 nm or more and 30 nmor less. By defining in this way, the cutting tool can be furtherexcellent in thermal cracking resistance.

[4] Preferably, the coating layer has a thickness with an average valueof 0.1 μm or more and 10 μm or less. By defining in this way, thecutting tool can further be excellent in wear resistance.

[5] Preferably, the cutting tool further comprises an underlying layerprovided between the substrate and the coating layer, wherein

the underlying layer is composed of a compound consisting of: at leastone element selected from the group consisting of a group 4 element, agroup 5 element and a group 6 element of the periodic table andaluminum; and at least one element selected from the group consisting ofcarbon, nitrogen, oxygen and boron, and

the underlying layer is different in composition from the first unitlayer, the second unit layer, and the lone layer. By defining in thisway, the cutting tool can have excellent thermal cracking resistance andexcellent wear resistance and, in addition thereto, the coating layerwith excellent peeling resistance.

[6] Preferably, the cutting tool further comprises a surface layerprovided on the coating layer, wherein

the surface layer is composed of a compound consisting of: at least oneelement selected from the group consisting of a group 4 element, a group5 element and a group 6 element of the periodic table and aluminum; andat least one element selected from the group consisting of carbon,nitrogen, oxygen and boron, and

the surface layer is different in composition from the first unit layer,the second unit layer, and the lone layer. By defining in this way, thecutting tool can be further excellent in wear resistance.

Detailed Description of Embodiments of the Present Disclosure

Hereinafter, an embodiment of the present disclosure (hereinafter alsoreferred to as “the present embodiment”) will be described. It should benoted, however, that the present embodiment is not exclusive. In thepresent specification, an expression in the form of “A to Z” means arange's upper and lower limits (that is, A or more and Z or less), andwhen A is not accompanied by any unit and Z is alone accompanied by aunit, A has the same unit as Z. Further, in the present specification,when a compound is represented by a chemical formula with itsconstituent elements' compositional ratio unspecified, such as “TiN,”the chemical formula shall encompass any conventionally knowncompositional ratio (or elemental ratio). The chemical formula shallinclude not only a stoichiometric composition but also anonstoichiometric composition. For example, the chemical formula of“TiN” includes not only a stoichiometric composition of “Ti₁N₁” but alsoa non-stoichiometric composition for example of “Ti₁N_(0.8).” This alsoapplies to descriptions for compounds other than “TiN.”

<<Cutting Tool>>

The presently disclosed cutting tool is

a cutting tool comprising a substrate and a coating layer provided onthe substrate,

the coating layer including a multilayer structure layer composed of afirst unit layer and a second unit layer, and a lone layer,

the first unit layer and the second unit layer being alternatelystacked,

the multilayer structure layer and the lone layer being stacked suchthat more than one multilayer structure layer and more than one lonelayer are alternately stacked,

the first unit layer including cubic Al_(x)Ti_(1-x)N crystal grains,

the second unit layer including cubic Al_(y)Ti_(1-y)N crystal grains,

the lone layer including cubic Ti_(z)Al_(1-z)N crystal grains,

an atomic ratio x of Al in the Al_(x)Ti_(1-x)N being 0.8 or more and0.95 or less,

an atomic ratio y of Al in the Al_(y)Ti_(1-y)N being 0.7 or more andless than 0.8,

an atomic ratio z of Ti in the Ti_(z)Al_(1-z)N being 0.55 or more and0.7 or less,

the first unit layer having a thickness with an average value of 2.5 nmor more and 5 nm or less,

the second unit layer having a thickness with an average value of 2.5 nmor more and 5 nm or less,

the multilayer structure layer having a thickness with an average valueof 10 nm or more and 45 nm or less,

the lone layer having a thickness with an average value of 2.5 nm ormore and 10 nm or less,

one multilayer structure layer and one lone layer forming a repetitiveunit having a thickness with an average value of 20 nm or more and 50 nmor less, a maximum value of 40 nm or more and 60 nm or less, and aminimum value of 10 nm or more and 30 nm or less.

A cutting tool 100 of the present embodiment comprises a substrate 10,and a coating layer 20 provided on substrate 10 (hereinafter also simplyreferred to as a “cutting tool”) (see FIG. 2). In addition to coatinglayer 20, cutting tool 100 may further comprise an underlying layer 13provided between substrate 10 and coating layer 20 (see FIG. 3). Cuttingtool 100 may further comprise a surface layer 14 provided on coatinglayer 20 (see FIG. 3). Other layers such as underlying layer 13 andsurface layer 14 will be described hereinafter.

The above-described layers provided on substrate 10 may be collectivelyreferred to as a “coating.” That is, cutting tool 100 comprises acoating 30 provided on substrate 10, and the coating includes coatinglayer 20. Further, coating 30 may further include underlying layer 13 orsurface layer 14.

The cutting tool can for example be a drill, an end mill (e.g., a ballend mill), an indexable cutting insert for a drill, an indexable cuttinginsert for an end mill, an indexable cutting insert for milling, anindexable cutting insert for turning, a metal saw, a gear cutting tool,a reamer, a tap, or the like.

FIG. 1 is a perspective view of one embodiment of the cutting tool byway of example. The cutting tool having such a shape is used as, forexample, an indexable cutting insert. Cutting tool 100 has a rake face1, a flank face 2, and a cutting edge ridge portion 3 where rake face 1and flank face 2 meet each other. That is, rake face 1 and flank face 2are faces that are connected with cutting edge ridge portion 3interposed therebetween. Cutting edge ridge portion 3 constitutes a tipof the cutting edge of cutting tool 100. Such a shape of cutting tool100 can also be understood as a shape of a substrate of the cuttingtool. That is, the substrate has a rake face, a flank face, and acutting edge ridge portion connecting the rake face and the flank facetogether.

<Substrate>

The substrate of the present embodiment can be any substrateconventionally known as a substrate of this type. For example, itpreferably includes at least one selected from the group consisting of acemented carbide (for example, a tungsten carbide (WC)-base cementedcarbide, a cemented carbide containing WC and, in addition, Co, acemented carbide containing WC with a carbonitride of Cr, Ti, Ta, Nb, orthe like added, and the like), a cermet (mainly composed of TiC, TiN,TiCN, or the like), a high-speed steel, ceramics (titanium carbide,silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, andthe like), a cubic boron nitride sintered material (a cBN sinteredmaterial), and a diamond sintered material.

Of these various types of substrates, it is particularly preferable toselect a cemented carbide (a WC-base cemented carbide, in particular) ora cermet (a TiCN-base cermet, in particular). This is because thesesubstrates are particularly excellent in balance between hardness andstrength at high temperature, in particular, and present excellentcharacteristics as a substrate for a cutting tool for theabove-described applications.

When using a cemented carbide as a substrate, the effect of the presentembodiment is exhibited even if the cemented carbide has a structureincluding free carbon or an extraordinary phase referred to as η phase.Note that the substrate used in the present embodiment may have itssurface modified. For example, for the cemented carbide, the surface maybe provided with a β-free layer, and for the cermet, the surface may beprovided with a surface hardened layer, and even if the surface ismodified in this way, the effect of the present embodiment is exhibited.

<Coating>

A coating according to the present embodiment includes a coating layerprovided on the substrate. The “coating” coats at least a part of thesubstrate (for example, a rake face that comes into contact with chipsduring a cutting process, a flank face that comes into contact with aworkpiece, and the like) to exhibit a function to improve the cuttingtool's various characteristics such as breaking resistance, wearresistance, impact resistance, and oxidation resistance. The coating ispreferably applied not only to a part of the substrate but also to theentire surface of the substrate. However, even if the substrate ispartially uncoated with the coating or the coating is partiallydifferent in configuration, such does not depart from the scope of thepresent embodiment.

The coating preferably has a thickness of 0.1 μm or more and 30 μm orless, more preferably 2 μm or more and 20 μm or less. In one aspect ofthe present embodiment, the coating may have a thickness of 0.1 μm ormore and 10 μm or less, and the coating may have a thickness of 2 μm ormore and 10 μm or less. Note that the thickness of the coating means atotal thickness of any layers constituting the coating. A “layerconstituting the coating” for example includes a coating layer (amultilayer structure layer and a lone layer), an underlying layer, asurface layer, and the like, as will be described hereinafter. Forexample, the thickness of the coating can be measured by measuring 10points selected, as desired, in a sample in a cross section parallel tothe direction of a normal to a surface of the substrate with a scanningtransmission electron microscope (STEM), and calculating an averagevalue of the measured 10 points in thickness. In doing so, a numericalvalue which seems to be an apparently unexpected value is excluded. Inone aspect of the present embodiment, the “thickness of the coating” canalso be understood as an average value in thickness of the coating. Thesame applies when measuring in thickness the coating layer (multilayerstructure layer and lone layer), underlying layer, surface layer and thelike described hereinafter. The scanning transmission electronmicroscope is JEM-2100F (trade name) manufactured by JEOL Ltd., forexample.

(Coating Layer)

The coating layer in the present embodiment is provided on thesubstrate. Note that being “provided on the substrate” is not limited tobeing provided directly on the substrate and also includes beingprovided on the substrate via another layer. That is, the coating layermay be provided directly on the substrate or may be provided on thesubstrate via another layer such as an underlying layer describedhereinafter insofar as such does not impair an effect of the presentdisclosure. The coating layer may be provided thereon with another layersuch as a surface layer. The coating layer may be an outermost surfacelayer of the coating.

The coating layer includes a multilayer structure layer composed of afirst unit layer and a second unit layer, and a lone layer. Themultilayer structure layer and the lone layer are stacked such that morethan one multilayer structure layer and more than one lone layer arealternately stacked. In one aspect of the present embodiment, thecoating layer may have a lowermost layer composed of the multilayerstructure layer or the lone layer. In another aspect of the presentembodiment, the coating layer may have an uppermost layer composed ofthe multilayer structure layer or the lone layer. As used herein, a“lowermost layer” means a layer of those configuring the coating layerthat is closest to the substrate. As used herein, an “uppermost layer”means a layer of those configuring the coating layer that is farthestfrom the substrate.

The coating layer preferably has a thickness with an average value of0.1 μm or more and 10 μm or less, more preferably 2 μm or more and 10 μmor less. The coating layer's average value in thickness can be confirmedby observing a vertical cross section of the substrate and the coatingwith a STEM in a method similar to that described above. Hereinafter,the multilayer structure layer and the lone layer that configure thecoating layer will be described.

(Multilayer Structure Layer)

The multilayer structure layer is composed of a first unit layer and asecond unit layer. The first unit layer and the second unit layer arealternately stacked. In one aspect of the present embodiment, themultilayer structure layer may have a lowermost layer composed of thefirst unit layer or the second unit layer. In another aspect of thepresent embodiment, the multilayer structure layer may have an uppermostlayer composed of the first unit layer or the second unit layer. As usedherein, a “lowermost layer” means a layer of those configuring themultilayer structure layer that is closest to the substrate. As usedherein, an “uppermost layer” means a layer of those configuring themultilayer structure layer that is farthest from the substrate.

The multilayer structure layer has a thickness with an average value of10 nm or more and 45 nm or less, preferably 15 nm or more and 45 nm orless. The multilayer structure layer's average value in thickness isdetermined as follows: Initially, a method similar to that describedabove is used to observe a vertical cross section of the substrate andthe coating with a STEM to determine each multilayer structure layer'sthickness. Subsequently, an average value in thickness of the multilayerstructure layers (that is, an average value of a plurality of multilayerstructure layers) is determined, and this average value is defined as anaverage value in thickness of the multilayer structure layer.

(First Unit Layer)

The first unit layer includes cubic Al_(x)Ti_(1-x)N crystal grains. Thatis, the first unit layer is a layer including a polycrystal having acomposition of Herein, the chemical formula of “Al_(x)Ti_(1-x)N” has acompositional ratio (or an elemental ratio) of “Al_(x)Ti_(1-x)” and “N”including not only a stoichiometric composition (e.g., (Al_(x)Ti_(1-x))but also a non-stoichiometric composition (e.g.,(Al_(x)Ti_(1-x))₁N_(0.8)). “Al_(y)Ti_(1-y)N” and “Ti_(z)Al_(1-z)N”described hereinafter are similarly discussed. An atomic ratio x of Alin the Al_(x)Ti_(1-x)N is 0.8 or more and 0.95 or less, preferably 0.8or more and 0.9 or less. The atomic ratio x can be determined byanalyzing crystal grains in the first unit layer appearing in a samplein the above-described cross section with an energy dispersive X-ray(EDX) spectrometer accompanying a transmission electron microscope(TEM). The atomic ratio x of Al thus determined is a value determined asan average of all of the crystal grains of the Al_(x)Ti_(1-x)N.Specifically, 10 points selected, as desired, in the first unit layer ina sample in the above-described cross section is each measured to obtaina value of an atomic ratio of Al, and an average value of such valuesobtained at the 10 points is defined as an atomic ratio of Al in theAl_(x)Ti_(1-x)N. In doing so, a numerical value which seems to be anapparently unexpected value is excluded. Herein, “10 points selected asdesired” are selected from different crystal grains of the first unitlayer.

When the multilayer structure layer includes two or more first unitlayers, then, initially, the above method is used to determine an atomicratio of Al in each first unit layer and an average value of the atomicratios of Al obtained from the first unit layers is defined as an atomicratio of Al in the first unit layer. When the multilayer structure layerincludes more than 10 first unit layers, any 10 first unit layers areselected and the above method is used to determine an atomic ratio of Alin each of the 10 first unit layers, and an average value of the atomicratios of Al determined from the 10 first unit layers is defined as anatomic ratio of Al in the first unit layer.

In the present embodiment, the coating layer includes two or moremultilayer structure layers. Accordingly, initially, the above method isused to determine an atomic ratio of Al of first unit layers in eachmultilayer structure layer and an average value of atomic ratios of Alobtained from the multilayer structure layers is defined as an atomicratio x of Al in the first unit layers. When the coating layer includesmore than 10 multilayer structure layers, any 10 multilayer structurelayers are selected and the above method is used to determine an atomicratio of Al of first unit layers in each of the 10 multilayer structurelayers, and an average value of the atomic ratios of Al determined fromthe 10 multilayer structure layers is defined as an atomic ratio x of Alin the first unit layer.

The EDX device is JED-2300 (trade name) manufactured by JEOL Ltd., forexample. Not only the atomic ratio of Al but those of Ti and N can alsobe calculated in the above method. The second unit layer and the lonelayer described hereinafter can also have their atomic ratios of Al, Ti(titanium), and N (nitrogen) calculated in the above-described method.

The first unit layer includes cubic Al_(x)Ti_(1-x)N crystal grains. Thefirst unit layer may further include hexagonal Al_(x)Ti_(1-x)N crystalgrains insofar as it exhibits an effect of the present disclosure. Thecubic Al_(x)Ti_(1-x)N crystal grains and the hexagonal Al_(x)Ti_(1-x)Ncrystal grains are identified by, for example, a pattern of adiffraction peak obtained through x-ray diffraction describedhereinafter.

When a total amount of crystal grains of cubic Al_(x)Ti_(1-x)N (c) andcrystal grains of hexagonal Al_(x)Ti_(1-x)N (h) serves as a reference,the crystal grains of hexagonal Al_(x)Ti_(1-x)N may be contained at aproportion (h/(c+h)) of 0% by volume or more and 15% by volume or lessand may be 0% by volume or more and 10% by volume or less. Theproportion can be determined for example by analyzing a pattern of adiffraction peak obtained through x-ray diffraction. A specific methodis employed, as follows:

An X-ray spectrum of the first unit layer in a sample in theabove-described cross section is obtained using an X-ray diffractometer(“MiniFlex600” (trade name) manufactured by Rigaku Corporation). TheX-ray diffractometer is used for example under the following conditions:

Characteristic X-ray: Cu-Kα (wavelength: 1.54 angstrom)

Tube voltage: 45 kV

Tube current: 40 mA

Filter: Multi-layer mirror

Optical system: Focusing method

X-ray diffractometry: θ-2θ method

In the obtained X-ray spectrum, cubic Al_(x)Ti_(1-x)N's peak intensity(Ic) and hexagonal Al_(x)Ti_(1-x)N's peak intensity (Ih) are measured.Herein, a “peak intensity” means a peak's height (cps) in the X-rayspectrum. Cubic Al_(x)Ti_(1-x)N's peak can be confirmed arounddiffraction angles 20=38° and 44°. Hexagonal Al_(x)Ti_(1-x)N's peak canbe confirmed around a diffraction angle 20=33°. A peak intensity is avalue excluding a background.

When a total amount of the cubic Al_(x)Ti_(1-x)N and the hexagonalAl_(x)Ti_(1-x)N serves as a reference, the hexagonal Al_(x)Ti_(1-x)N iscontained at a proportion (vol %), as calculated by an expressionindicated hereinafter. The cubic Al_(x)Ti_(1-x)N's peak intensity (Ic)is obtained by a sum of a peak intensity around 2θ=38° and a peakintensity around 2θ=44°.Proportion of the hexagonal Al_(x)Ti_(1-x)N contained (vol%)=100×{Ih/(Ih+Ic)}

While a method for analyzing a crystal form of crystal grains in thefirst unit layer has been described above, a similar method can also beused to analyze a crystal form of crystal grains in each of the secondunit layer and the lone layer described hereinafter.

The first unit layer has a thickness with an average value of 2.5 nm ormore and 5 nm or less, preferably 3 nm or more and 5 nm or less. Thefirst unit layer's average value in thickness can be determined asfollows: a STEM is used to measure 10 points selected, as desired, inthe same layer in a sample in a cross section parallel to the directionof a normal to a surface of the substrate and an average value of themeasured 10 points in thickness is calculated to determine the firstunit layer's average value in thickness. In doing so, a numerical valuewhich seems to be an apparently unexpected value is excluded. When themultilayer structure layer includes two or more first unit layers, then,initially, the above method is used to determine an average value inthickness of each first unit layer and an average value of thedetermined values (that is, an average value of a plurality of firstunit layers) is defined as an average value in thickness of the firstunit layers in the multilayer structure layer. When the multilayerstructure layer includes more than 10 first unit layers, any 10 firstunit layers are selected and the above method is used to determine anaverage value in thickness of each of the 10 first unit layers, and anaverage value of the values determined from the 10 first unit layers isdefined as an average value in thickness of the more than 10 first unitlayers in the multilayer structure layer.

In the present embodiment, the coating layer includes two or moremultilayer structure layers. Accordingly, initially, the above method isused to determine an average value in thickness of first unit layers ineach multilayer structure layer and an average value of such averagevalues obtained from the multilayer structure layers is defined as anaverage value in thickness of the first unit layers. When the coatinglayer includes more than 10 multilayer structure layers, any 10multilayer structure layers are selected and the above method is used todetermine an average value in thickness of first unit layers in each ofthe 10 multilayer structure layers, and an average value of such averagevalues determined from the 10 multilayer structure layers is defined asan average value in thickness of the first unit layers. The same applieswhen measuring in thickness a second unit layer and a lone layerdescribed hereinafter.

(Second Unit Layer)

The second unit layer includes cubic Al_(y)Ti_(1-y)N crystal grains.That is, the second unit layer is a layer including a polycrystal havinga composition of Al_(y)Ti_(1-y)N. An atomic ratio y of Al in theAl_(y)Ti_(1-y)N is 0.7 or more and less than 0.8, preferably 0.75 ormore and less than 0.8. The atomic ratio y can be determined in a methodsimilar to that described above, that is, by analyzing crystal grains inthe second unit layer appearing in a sample in cross section with an EDXdevice accompanying a TEM.

The second unit layer includes cubic Al_(y)Ti_(1-y)N crystal grains. Thesecond unit layer may further include hexagonal Al_(y)Ti_(1-y)N crystalgrains insofar as it exhibits an effect of the present disclosure. Thecubic Al_(y)Ti_(1-y)N crystal grains and the hexagonal Al_(y)Ti_(1-y)Ncrystal grains are identified by, for example, a pattern of adiffraction peak obtained through x-ray diffraction in a method similarto that described above.

When a total amount of crystal grains of cubic Al_(y)Ti_(1-y)N (c) andcrystal grains of hexagonal Al_(y)Ti_(1-y)N (h) serves as a reference,the crystal grains of hexagonal Al_(y)Ti_(1-y)N may be contained at aproportion (h/(c+h)) of 0% by volume or more and 15% by volume or lessand may be so at a proportion of 0% by volume or more and 10% by volumeor less. The proportion can be determined for example by analyzing apattern of a diffraction peak obtained through x-ray diffraction in amethod similar to that described above.

The second unit layer has a thickness with an average value of 2.5 nm ormore and 5 nm or less, preferably 3 nm or more and 5 nm or less. Thesecond unit layer's average value in thickness can be determined with aSTEM in a method similar to that described above.

(Lone Layer)

The lone layer includes cubic Ti_(z)Al_(1-z)N crystal grains. That is,the lone layer is a layer including a polycrystal having a compositionof Ti_(z)Al_(1-z)N. An atomic ratio z of Ti in the Ti_(z)Al_(1-z)N is0.55 or more and 0.7 or less, preferably 0.6 or more and 0.7 or less.The lone layer having an atomic ratio z in the above range has aconfiguration having a higher atomic ratio of titanium than themultilayer structure layer does. The atomic ratio z can be determined ina method similar to that described above, that is, by analyzing crystalgrains in the lone layer appearing in the sample in cross section withan EDX device accompanying a TEM.

The lone layer includes cubic Ti_(z)Al_(1-z)N crystal grains. The lonelayer may further include hexagonal Ti_(z)Al_(1-z)N crystal grainsinsofar as it exhibits an effect of the present disclosure. The cubicTi_(z)Al_(1-z)N crystal grains and the hexagonal Ti_(z)Al_(1-z)N crystalgrains are identified by a pattern of a diffraction peak obtainedthrough x-ray diffraction in a method similar to that described above.

When a total amount of crystal grains of cubic Ti_(z)Al_(1-z)N (c) andcrystal grains of hexagonal Ti_(z)Al_(1-z)N (h) serves as a reference,the crystal grains of hexagonal Ti_(z)Al_(1-z)N may be contained at aproportion (h/(c+h)) of 0% by volume or more and 15% by volume or less,and may be so at a proportion of 0% by volume or more and 10% by volumeor less. The proportion can be determined by analyzing a pattern of adiffraction peak obtained through x-ray diffraction in a method similarto that described above.

The lone layer has a thickness with an average value of 2.5 nm or moreand 10 nm or less, preferably 2.5 nm or more and 5 nm or less. The lonelayer's average value in thickness can be determined with a STEM in amethod similar to that described above.

(Repetitive Unit of Multilayer Structure Layer and Lone Layer)

One multilayer structure layer and one lone layer form a repetitive unithaving a thickness with an average value of 20 nm or more and 50 nm orless, a maximum value of 40 nm or more and 60 nm or less, and a minimumvalue of 10 nm or more and 30 nm or less. As the repetitive unit is thusconfigured the coating layer tends to introduce strain and stressbetween lone layers. As a result, the present inventors consider thatthe coating layer has enhanced thermal cracking resistance. The coatinglayer according to the present embodiment is formed by alternatelystacking the multilayer structure layer and the lone layer, and acombination of one multilayer structure layer and one lone layeradjacent to each other will be hereinafter referred to as a “repetitiveunit composed of one multilayer structure layer and one lone layer” orsimply a “repetitive unit.” In the repetitive unit, the layers arestacked in the following order: as seen at the substrate, the lone layeris deposited and thereon the multilayer structure layer is deposited. A“thickness of the repetitive unit” means a sum in thickness of amultilayer structure layer and a lone layer configuring a repetitiveunit. Note that when the coating layer has a lowermost layer which isthe multilayer structure layer, the multilayer structure layer of thelowermost layer is not considered in determining the repetitive unit'saverage, maximum and minimum values in thickness described hereinafter.

Conventionally, attempts have been made to improve cutting tools incutting performance by forming a layer that configures a coating in amultilayer structure. However, optimal cutting performance requiredvaries depending on the material of the workpiece to be cut, and therehas been a demand for further improvement of cutting tools. Under suchcircumstances, the present inventors have diligently conducted studies,and as a result found that a cutting tool's various characteristics (forexample, impact resistance, oxidation resistance, wear resistance,thermal crack resistance, and the like) can be adjusted by varying thelone layer and the repetitive unit in thickness.

The cutting tool according to the present embodiment has the repetitiveunit configured as described above, and can thus have excellent thermalcracking resistance and excellent wear resistance. The cutting tool isparticularly suitable as a cutting tool used for high-speed processingof spheroidal graphite cast iron (e.g., FCD600).

The repetitive unit has a thickness with an average value of 20 nm ormore and 50 nm or less, preferably 25 nm or more and 50 nm or less. Therepetitive unit's average value in thickness can be determined by a sumof an average value in thickness of the multilayer structure layer andan average value in thickness of the lone layer. When the coating layerincludes more than 10 repetitive units, 10 successive repetitive unitsare selected in the coating layer, and an average value of the selected10 repetitive units is defined as an average value in thickness of themore than 10 repetitive units. In doing so, the 10 layers are selectedsuch that the interface between the fourth layer and the fifth layer inthe selected 10 layers is closest to the center of the coating layer.

The repetitive unit has a thickness with a maximum value of 40 nm ormore and 60 nm or less, preferably 50 nm or more and 60 nm or less. Themaximum value in thickness can be determined in the following method:Initially, a method similar to that describe above is used to determinea thickness of each repetitive unit in a sample in the above-describedcross section with a STEM. Subsequently, the repetitive units arecompared in thickness and a maximum value thereof is defined as amaximum value in thickness of the repetitive units. When the coatinglayer includes more than 10 repetitive units, 10 successive repetitiveunits are selected in the coating layer, and a maximum value in theselected 10 repetitive units is defined as a maximum value in thicknessof the more than 10 repetitive units. In doing so, the 10 layers areselected such that the interface between the fourth layer and the fifthlayer in the selected 10 layers is closest to the center of the coatinglayer. In comparing repetitive units in thickness, a numerical valuewhich seems to be an apparently unexpected value is excluded.

The repetitive unit has a thickness with a minimum value of 10 nm ormore and 30 nm or less, preferably 12 nm or more and 30 nm or less. Theminimum value in thickness can be determined in the following method:Initially, a method similar to that describe above is used to determinea thickness of each repetitive unit in a sample in the above-describedcross section with a STEM. Subsequently, the repetitive units arecompared in thickness and a minimum value thereof is defined as aminimum value in thickness of the repetitive units. When the coatinglayer includes more than 10 repetitive units, 10 successive repetitiveunits are selected in the coating layer, and a minimum value of theselected 10 repetitive units is defined as a minimum value in thicknessof the more than 10 repetitive units. In doing so, the 10 layers areselected such that the interface between the fourth layer and the fifthlayer in the selected 10 layers is closest to the center of the coatinglayer. In comparing repetitive units in thickness, a numerical valuewhich seems to be an apparently unexpected value is excluded.

In one aspect of the present embodiment, the repetitive unit preferablyhas a thickness with an average value of 25 nm or more and 50 nm orless, a maximum value of 50 nm or more and 60 nm or less, and a minimumvalue of 12 nm or more and 30 nm or less.

(Underlying Layer)

Preferably, the coating further includes an underlying layer providedbetween the substrate and the coating layer, and the underlying layer iscomposed of a compound consisting of at least one element selected fromthe group consisting of a group 4 element, a group 5 element and a group6 element of the periodic table and aluminum (Al) and at least oneelement selected from the group consisting of carbon, nitrogen, oxygenand boron. The underlying layer is different in composition from thefirst unit layer, the second unit layer, and the lone layer. Examples ofthe group 4 element of the periodic table include titanium (Ti),zirconium (Zr), hafnium (Hf), and the like. Examples of the group 5element of the periodic table include vanadium (V), niobium (Nb),tantalum (Ta), and the like. Examples of the group 6 element of theperiodic table include chromium (Cr), molybdenum (Mo), tungsten (W), andthe like. The underlying layer is preferably composed of a compoundrepresented by TiN or TiCN. Such an underlying layer exhibits strongadhesion to both the coating layer and the substrate. As a result, thecoating is enhanced in peeling resistance.

The underlying layer preferably has a thickness with an average value of0.1 μm or more and 20 μm or less, more preferably 1 μm or more and 15 μmor less. Such a thickness can be confirmed by observing a vertical crosssection of the substrate and the coating with a STEM in a method similarto that described above.

(Surface Layer)

Preferably, the coating further includes a surface layer provided on thecoating layer and the surface layer is composed of a compound consistingof at least one element selected from the group consisting of a group 4element, a group 5 element and a group 6 element of the periodic tableand aluminum (Al) and at least one element selected from the groupconsisting of carbon, nitrogen, oxygen and boron. The surface layer isdifferent in composition from the first unit layer, the second unitlayer, and the lone layer. The compound included in the surface layerincludes TiN, Al₂O₃ and AlN for example.

The surface layer preferably has a thickness with an average value of0.1 μm or more and 3 μm or less, more preferably 0.3 μm or more and 2 μmor less. Such a thickness can be confirmed by observing a vertical crosssection of the substrate and the coating with a STEM in a method similarto that described above.

(Another Layer)

The coating may further include another layer insofar as the cuttingtool according to the present embodiment exhibits the above-describedeffect. The other layer may have a composition different from oridentical to that of the coating layer, the underlying layer, or thesurface layer. Examples of a compound included in the other layerinclude TiN, TiCN, TiBN, and Al₂O₃. The other layer is not limited,either, in in what order it is stacked. For example, the other layer maybe provided between the underlying layer and the coating layer. Whilethe other layer is not particularly limited in thickness as long as itexhibits an effect of the present embodiment, it is for example 0.1 μmor more and 20 μm or less.

<<Method for Manufacturing the Cutting Tool>>

A method for manufacturing a cutting tool according to the presentembodiment comprises:

preparing the substrate (hereinafter also simply referred to as a “firststep”); and

forming the coating layer on the substrate through chemical vapordeposition (hereinafter also simply referred to as a “second step”),

the step of forming the coating layer on the substrate including jettinga first gas, a second gas and a third gas onto the substrate in anatmosphere of 650° C. or higher and 900° C. or lower and 0.5 kPa orhigher and 30 kPa or lower, the first gas including a gas of a halide ofaluminum and a gas of a halide of titanium, the second gas including agas of a halide of aluminum, a gas of a halide of titanium and a gas ofammonia, the third gas including a gas of ammonia.

<First Step: Step of Preparing a Substrate>

In the first step, a substrate is prepared. For example, a cementedcarbide substrate is prepared as the substrate. The cemented carbidesubstrate may be a commercially available product or may be manufacturedin a typical powder metallurgy method. When the substrate ismanufactured in a typical powder metallurgy method, for example, WCpowder and Co powder or the like are mixed using a ball mill or the liketo obtain a powdery mixture. After the powdery mixture is dried, it isshaped into a prescribed shape (for example, SEET13T3AGSN-G, etc.) toobtain a shaped body.

The shaped body is sintered to obtain a WC—Co based cemented carbide (asintered material). Subsequently, the sintered material can be honed orsubjected to a prescribed cutting edge process to prepare a substratemade of the WC—Co based cemented carbide. In the first step, any othersubstrate may be prepared insofar as it is a substrate conventionallyknown as a substrate of this type.

<Second Step: Forming the Coating Layer on the Substrate ThroughChemical Vapor Deposition>

In the second step, the coating layer is formed on the substrate throughchemical vapor deposition. More specifically, in the second step, afirst gas, a second gas and a third gas are jetted onto the substrate inan atmosphere of 650° C. or higher and 900° C. or lower and 0.5 kPa orhigher and 30 kPa or lower, the first gas including a gas of a halide ofaluminum and a gas of a halide of titanium, the second gas including agas of a halide of aluminum, a gas of a halide of titanium and a gas ofammonia, the third gas including a gas of ammonia. This step can beperformed using, for example, a CVD apparatus described below.

(CVD Apparatus)

FIG. 4 is a schematic cross section of one example of a CVD apparatusused for manufacturing the cutting tool according to the presentembodiment. As shown in FIG. 4, a CVD apparatus 50 includes a pluralityof substrate setting jigs 52 for setting substrate 10, and a reactionchamber 53 made of heat-resistant alloy steel and incorporatingsubstrate setting jigs 52 therein. A temperature controller 54 isprovided around reaction chamber 53 for controlling the temperatureinside reaction chamber 53. In the present embodiment, for example,substrate 10 is preferably set such that a metal skewer (not shown)radially extending from gas introduction pipe 58 passes through athroughhole of substrate 10.

A gas introduction pipe 58 having a first gas introduction pipe 55, asecond gas introduction pipe 56 and a third gas introduction pipe 57adjacently bonded together extends in the vertical direction through aspace inside reaction chamber 53 rotatably about the vertical direction.Gas introduction pipe 58 is configured such that the first gasintroduced into first gas introduction pipe 55, the second gasintroduced into second gas introduction pipe 56, and the third gasintroduced into third gas introduction pipe 57 are not mixed togetherinside gas introduction pipe 58 (see FIG. 5). Further, first gasintroduction pipe 55, second gas introduction pipe 56, and third gasintroduction pipe 57 are each provided with a plurality of throughholesfor jetting the gases respectively flowing through first, second andthird gas introduction pipes 55, 56 and 57 onto substrate 10 set onsubstrate setting jig 52. In the present embodiment, the gas jettingthrough hole is preferably set in number such that two through holes areassociated with one metal skewer extending radially from gasintroduction pipe 58. The through hole thus set allows the lone layerand the repetitive unit to be deposited as desired in thickness.

Further, reaction chamber 53 is provided with a gas exhaust pipe 59 forexternally exhausting the gas inside reaction chamber 53, and the gas inreaction chamber 53 passes through gas exhaust pipe 59 and is exhaustedout of reaction chamber 53 via a gas exhaust port 60.

More specifically, the first gas, the second gas and the third gas areintroduced into first gas introduction pipe 55, second gas introductionpipe 56 and third gas introduction pipe 57, respectively. In doing so,the first, second and third gases in their respective gas introductionpipes may have any temperature that does not liquefy the gases.Subsequently, the first gas, the second gas and the third gas are jettedin this order repeatedly into reaction chamber 53 with an atmosphere settherein to have a temperature of 650° C. or higher and 900° C. or lower(preferably 700° C. or higher and 780° C. or lower) and a pressure of0.5 kPa or higher and 30 kPa or lower (preferably 2 kPa or higher and 5kPa or lower). As gas introduction pipe 58 has the plurality ofthroughholes, the first, second, and third gases introduced are jettedinto reaction chamber 53 through different throughholes, respectively.While the gases are thus jetted, gas introduction pipe 58 is rotating ata rotation speed for example of 2 to 4 rpm about the above-describedaxis, as indicated in FIG. 4 by a rotating arrow. As a result, the firstgas, the second gas, and the third gas can be jetted in this orderrepeatedly onto substrate 10.

(First Gas)

The first gas includes a gas of a halide of aluminum and a gas of ahalide of titanium.

Examples of the gas of a halide of aluminum include a gas of aluminumchloride (a gas of AlCl₃ and a gas of Al₂Cl₆). Preferably, a gas ofAlCl₃ is used. The gas of a halide of aluminum preferably has aconcentration (% by volume) of 0.3% by volume or more and 1.5% by volumeor less, more preferably 0.8% by volume or more and 0.87% by volume orless with reference to the total volume of the first gas.

Examples of the gas of a halide of titanium include a gas of titanium(IV) chloride (a gas of TiCl₄), a gas of titanium (III) chloride (a gasof TiCl₃), and the like. Preferably a gas of titanium (IV) chloride isused. The gas of a halide of titanium preferably has a concentration (in% by volume) of 0.1% by volume or more and 1% by volume or less, morepreferably 0.1% by volume or more and 0.2% by volume or less withreference to the total volume of the first gas.

In the first gas, the gas of a halide of aluminum has a molar ratiopreferably of 0.5 or more and 0.9 or less, more preferably 0.8 or moreand 0.87 or less with reference to the total moles of the gas of ahalide of aluminum and the gas of a halide of titanium.

The first gas may include a gas of hydrogen and may include an inert gassuch as a gas of argon. The inert gas preferably has a concentration (%by volume) of 5% by volume or more and 70% by volume or less, morepreferably 15% by volume or more and 60% by volume or less, still morepreferably 15% by volume or more and 20% by volume or less withreference to the total volume of the first gas. The gas of hydrogentypically occupies the balance of the first gas.

The first gas is jetted onto the substrate at a flow rate preferably of20 to 50 L/min., more preferably 30 to 35 L/min.

(Second Gas)

The second gas includes a gas of a halide of aluminum, a gas of a halideof titanium, and a gas of ammonia. The gas of a halide of aluminum andthe gas of a halide of titanium can be the gases exemplified in theabove (First Gas) section. The gas of a halide of aluminum and the gasof a halide of titanium that are used for the first gas may be identicalto or different from the gas of a halide of aluminum and the gas of ahalide of titanium that are used for the second gas, respectively.

The gas of a halide of aluminum preferably has a concentration (% byvolume) of 2% by volume or more and 5% by volume or less, morepreferably 2% by volume or more and 3.25% by volume or less, still morepreferably 2% by volume or more and 2.5% by volume or less withreference to the total volume of the second gas.

The gas of a halide of titanium preferably has a concentration (in % byvolume) of 0.1% by volume or more and 3% by volume or less, morepreferably 1.75% by volume or more and 3% by volume or less, still morepreferably 2.5% by volume or more and 3% by volume or less withreference to the total volume of the second gas.

In the second gas, the gas of a halide of aluminum has a molar ratiopreferably exceeding 0.35 and less than 0.7, more preferably 0.4 or moreand 0.65 or less, still more preferably 0.4 or more and 0.5 or less withreference to the total moles of the gas of a halide of aluminum and thegas of a halide of titanium.

The gas of ammonia preferably has a concentration (% by volume) of 5% byvolume or more and 15% by volume or less, more preferably 9% by volumeor more and 11% by volume or less with reference to the total volume ofthe second gas.

The second gas may include a gas of hydrogen and may include an inertgas such as a gas of argon. The inert gas preferably has a concentration(% by volume) of 5% by volume or more and 50% by volume or less, morepreferably 15% by volume or more and 17% by volume or less withreference to the total volume of the second gas. The gas of hydrogentypically occupies the balance of the second gas.

The second gas is jetted onto the substrate at a flow rate preferably of20 to 40 L/min.

(Third Gas)

The third gas includes a gas of ammonia. The third gas may include a gasof hydrogen and may include an inert gas such as a gas of argon.

The gas of ammonia preferably has a concentration (% by volume) of 2% byvolume or more and 30% by volume or less, more preferably 2% by volumeor more and 10% by volume or less with reference to the total volume ofthe third gas. The gas of hydrogen typically occupies the balance of thethird gas.

The third gas is jetted onto the substrate at a flow rate preferably of10 to 20 L/min.

<Another Step>

In the manufacturing method according to the present embodiment, inaddition to the steps described above, an additional step may beperformed, as appropriate, insofar as the method exhibits an effect ofthe present embodiment. Examples of the additional step include the stepof forming an underlying layer between the substrate and the coatinglayer, the step of forming a surface layer on the coating layer, thestep of blasting the coating, and the like. The underlying layer and thesurface layer may be formed in any method, and the layers are formed forexample through CVD.

In the method for manufacturing a surface-coated cutting tool accordingto the present embodiment, the coating layer is formed through CVD. Whenthis is compared with forming the coating through PVD, the formerenhances the coating's adhesion to the substrate (or coating adhesion).

Examples

Hereinafter, the present invention will more specifically be describedwith reference to examples although the present invention is not limitedthereto.

<<Manufacturing a Cutting Tool>>

<Preparing a Substrate>

Initially, as a substrate on which a coating is to be formed, asubstrate composed of cemented carbide indicated in Table 1 below(hereinafter also simply referred to as a “substrate”) was prepared(i.e., a first step). Specifically, initially, powdery raw materials ofa blending composition (% by mass) shown in Table 1 were uniformlymixed. In Table 1, “balance” indicates that WC occupies the balance ofthe blending composition (% by mass).

TABLE 1 blending composition (mass %) type Co TiC Cr₃C₂ TaC WC substrate6.0 1 0.3 0.5 balance

Subsequently, the powdery mixture was pressure-formed into a prescribedshape and thereafter sintered for 1 to 2 hours at 1300 to 1500° C. toobtain the above substrate (substrate shape (JIS standard):SEET13T3AGSN-G). SEET13T3AGSN-G is a shape of an indexable cuttinginsert for a rotating tool.

<Depositing the Coating>

A coating was deposited on a surface of the substrate by depositing theunderlying layer, the coating layer and the surface layer shown in Table8 on the surface of the substrate. The coating was deposited mainlythrough CVD.

Hereinafter, a method for depositing each layer constituting the coatingwill be described.

(Depositing the Coating Layer)

Under the conditions shown in Table 2 for deposition, a first gas, asecond gas, and a third gas having the compositions shown in Tables 3, 4and 5, respectively, were jetted in this order repeatedly onto a surfaceof the substrate to form a coating layer (a second step). In doing so,the substrate was set such that a metal skewer radially extending fromthe gas introduction pipe passed through a throughhole of the substrate.Further, the gas jetting through hole was set in number such that twothrough holes were associated with one metal skewer extending radiallyfrom the gas introduction pipe. When an underlying layer was provided ona surface of the substrate, the coating layer was formed on a surface ofthe underlying layer.

For example, a coating layer indicated in Table 6-1 by an identificationsymbol [1] was deposited as follows: with a temperature of 780° C., apressure of 3 kPa, and the gas introduction pipe having a rotationalspeed of 4 rpm set as conditions for deposition (as indicated in Table 2by an identification symbol 2-b), a first gas indicated in Table 3 by anidentification symbol 3-e (0.85% by volume of AlCl₃, 0.15% by volume ofTiCl₄, 20% by volume of Ar, and a balance of H₂, with a gas flow rate of35 L/min), a second gas indicated in Table 4 by an identification symbol4-b (2% by volume of AlCl₃, 3% by volume of TiCl₄, 9% by volume of NH₃,15% by volume of Ar, and a balance of H₂, with a gas flow rate of 40L/min), and a third gas indicated in Table 5 by an identification symbol5-a (3% by volume of NH₃, and a balance is H₂, with a gas flow rate of20 L/min) were jetted in this order repeatedly onto a surface of thesubstrate to deposit the coating layer. A coating layer indicated inTable 6-2 by an identification symbol [20] was deposited in a known PVDmethod. Deposited coating layers each have a composition and the like,as shown in Tables 6-1 and 6-2.

TABLE 2 conditions for deposition ID symbol 2-b temperature (° C.) 780pressure (kPa) 3 rotational speed (rpm) 4

TABLE 3 composition of 1st gas ID symbol 3-a 3-b 3-c 3-d 3-e 3-f 3-g 3-hAlCl₃ (vol %) 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.85 TiCl₄ (vol %) 0.150.15 0.15 0.15 0.15 0.15 0.15 0.15 AlCl₃/(AlCl₃ + TiCl₄) 0.85 0.85 0.850.85 0.85 0.85 0.85 0.85 (molar ratio) Ar (vol %) 30 30 25 20 20 15 1510 H₂ (vol %) balance balance balance balance balance balance balancebalance gas flow rate (L/min) 55 50 40 40 35 35 30 20

TABLE 4 composition of 2nd gas ID symbol 4-a 4-b 4-c 4-d 4-e 4-f 4-g 4-hAlCl₃ (vol %) 1.75 2 2.25 2.5 2.75 3 3.25 3.5 TiCl₄ (vol %) 3.25 3 2.752.5 2.25 2 1.75 1.5 AlCl₃/(AlCl₃ + TiCl₄) 0.35 0.4 0.45 0.5 0.55 0.60.65 0.7 (molar ratio) NH₃ (vol %) 9 9 9 9 9 9 9 9 Ar (vol %) 15 15 1515 15 15 15 15 H₂ (vol %) balance balance balance balance balancebalance balance balance gas flow rate (L/min) 40 40 40 40 40 40 40 40

TABLE 5 composition of 3rd gas ID symbol 5-a NH₃ (vol %) 3 H₂ (vol %)balance gas flow rate (L/min) 20

TABLE 6-1 repetitive unit ID ID 1st unit layer 2nd unit layer total lonelayer symbol symbol atomic ratio thick- atomic ratio thick- thick-atomic ratio thick- ID in in h/(c + h) x of Al in ness* h/(c + h) y ofAl in ness* ness* h/(c + h) z of Ti in ness* symbol table 3 table 4 (vol%) Al_(x)Ti_(1-x)N (nm) (vol %) Al_(y)Ti_(1-y)N (nm) (nm) (vol %)Ti_(z)Al_(1-z)N (nm) [1] 3-e 4-b 3 0.83 2.6 4 0.73 2.8 18.4 2 0.56 8.1[2] 3-f 4-b 2 0.86 3.4 2 0.76 3.8 33.5 3 0.62 3.2 [3] 3-g 4-b 4 0.80 2.72 0.71 2.7 29.2 2 0.59 8.4 [4] 3-e 4-c 3 0.90 3.3 4 0.79 4.1 33.3 2 0.632.6 [5] 3-f 4-c 2 0.89 4.0 3 0.79 4.2 35.8 2 0.65 4.8 [6] 3-g 4-c 4 0.934.5 4 0.79 4.3 37.8 4 0.65 4.9 [7] 3-e 4-d 2 0.90 4.0 2 0.76 4.9 39.0 30.58 8.7 [8] 3-f 4-d 2 0.91 4.6 3 0.78 4.8 40.3 2 0.62 4.4 [9] 3-g 4-d 30.88 4.2 4 0.78 3.8 35.5 3 0.61 9.2 *average value in thickness

TABLE 6-2 repetitive unit multilayer structure layer ID ID 1st unitlayer 2nd unit layer total lone layer symbol symbol atomic ratio thick-atomic ratio thick- thick- atomic ratio thick- ID in in h/(c + h) x ofAl in ness* h/(c + h) y of Al in ness* ness* h/(c + h) z of Ti in ness*symbol table 3 table 4 (vol %) Al_(x)Ti_(1-x)N (nm) (vol %)Al_(y)Ti_(1-y)N (nm) (nm) (vol %) Ti_(z)Al_(1-z)N (nm) [10] 3-e 4-a 30.81 2.9 2 0.72 2.9 20.3 2 0.50 8.5 [11] 3-g 4-a 2 0.80 3.1 3 0.71 3.322.8 2 0.53 8.1 [12] 3-d 4-b 2 0.84 2.1 2 0.74 2.3 9.7 3 0.59 7.2 [13]3-h 4-b 2 0.85 5.8 2 0.75 6.5 60.6 3 0.59 16.3 [14] 3-d 4-d 3 0.86 1.8 40.76 1.8 7.6 2 0.56 6.7 [15] 3-h 4-d 3 0.85 5.5 3 0.75 5.8 47.4 3 0.5713.9 [16] 3-e 4-e 4 0.85 3.5 2 0.75 3.3 22.7 3 0.72 5.9 [17] 3-g 4-e 40.89 3.7 4 0.79 4.3 25.2 2 0.74 5.6 [18] — 4-c 3 0.86 3.6 2 0.76 4.75000 absent [19] 3-c — absent 2 0.57 5000 [20]** — — 2 0.63 3.3 4 0.6 4.9 5000 absent *average value in thickness **deposited through knownPVD.

(Depositing an Underlying Layer and Depositing a Surface Layer)

Under conditions indicated in Table 7 for deposition, a reactant gashaving a composition indicated in Table 7 was jetted onto a surface ofthe substrate to deposit an underlying layer. Under conditions indicatedin Table 7 for deposition, a reactant gas having a composition indicatedin Table 7 was jetted onto a surface of the coating layer to deposit asurface layer.

TABLE 7 conditions for deposition pressure temperature gas flow typecomposition of reactant gas (vol %) (kPa) (° C.) rate (L/min) TiN TiCl₄= 0.5%, N₂ = 41.2%, H₂ = balance 79.8 780 45.9 TiCN TiCl₄ = 2.0%, CH₃CN= 0.7%, H₂ = balance 9 860 50.5 Al₂O₃ AlCl₃ = 1.6%, CO₂ = 4.5%, H₂S =0.2%, NO₂ = 0.5%, 6.7 850 46.2 H₂ = balance

Cutting tools according to the present example were thus manufacturedthrough the above process. The cutting tools of Sample Nos. 1-3 and 2 to20 include a substrate, a coating layer provided on the substrate, andan underlying layer provided between the substrate and the coating layer(see table 8). The cutting tools of Sample Nos. 1-1 and 1-2 include asubstrate, an coating layer provided on the substrate, an underlyinglayer provided between the substrate and the coating layer, and asurface layer provided on the coating layer (see table 8).

<<Evaluating Characteristics of Cutting Tools>>

Using the cutting tools of the samples manufactured as described above,the cutting tools' characteristics were evaluated as follows: Thecutting tools of Sample Nos. 1-1 to 1-3 and 2 to 9 correspond toexamples. The cutting tools of Sample Nos. 10 to 20 correspond tocomparative examples.

<Measuring Thickness of Coating and the Like>

The coating and the underlying, coating and surface layers constitutingthe coating were measured in thickness by measuring each layer at any 10points selected, as desired, in a sample in a cross section parallel tothe direction of a normal to a surface of the substrate with a scanningtransmission electron microscope (STEM) (manufactured by JEOL Ltd.,trade name: JEM-2100F), and calculating an average value in thickness ofthe measured 10 points. A result is shown in Table 8. In the “surfacelayer” column, “-” indicates that the surface layer does not exist inthe coating. Furthermore, in the “coating layer” column, an indicationsuch as “[1] (3.6)” indicates that a coating layer has a configurationindicated in Table 6-1 by identification symbol [1] and has a thicknessof 3.6 μm. In Table 8, an indication such as “TiCN (0.5)” indicates thatthe corresponding layer is a TiCN layer having a thickness of 0.5 μm.Two compounds indicated in a single cell (for example, “Al₂O₃ (0.2)-TiN(0.1)”) indicate that the compound on the left side (Al₂O₃ (0.2)) is alayer located on a side closer to a surface of the substrate and thecompound on the right side (TiN (0.1)) is a layer located on a sidefarther from the surface of the substrate. Furthermore, an indicationsuch as “[Al₂O₃ (0.2)-TiN (0.1)]×3” or the like means that a layerrepresented by “Al₂O₃ (0.2)-TiN (0.1)” is deposited three timesrepeatedly.

TABLE 8 coating's configuration & each layer's thickness totalunderlying coating coating sample layer layer surface layer thicknessnos. (μm) (μm) (μm) (μm) 1-1 TiCN (0.5)  [1] (3.6) [Al₂O₃(0.2)-TiN(0.1)]× 3 5.0 1-2 TiCN (0.5)  [1] (4.5) Al₂O₃ (0.5) 5.5 1-3 TiCN (1.0)  [1](5.0) — 6.0 2 TiCN (1.0)  [2] (5.0) — 6.0 3 TiCN (1.0)  [3] (5.0) — 6.04 TiCN (1.0)  [4] (5.0) — 6.0 5 TiCN (1.0)  [5] (5.0) — 6.0 6 TiCN (1.0) [6] (5.0) — 6.0 7 TiCN (1.0)  [7] (5.0) — 6.0 8 TiCN (1.0)  [8] (5.0) —6.0 9 TiCN (1.0)  [9] (5.0) — 6.0 10 TiCN (1.0) [10] (5.0) — 6.0 11 TiCN(1.0) [11] (5.0) — 6.0 12 TiCN (1.0) [12] (5.0) — 6.0 13 TiCN (1.0) [13](5.0) — 6.0 14 TiCN (1.0) [14] (5.0) — 6.0 15 TiCN (1.0) [15] (5.0) —6.0 16 TiCN (1.0) [16] (5.0) — 6.0 17 TiCN (1.0) [17] (5.0) — 6.0 18TiCN (1.0) [18] (5.0) — 6.0 19 TiCN (1.0) [19] (5.0) — 6.0 20 TiCN (1.0)[20] (5.0) — 6.0

<Analyzing Multilayer Structure Layer and Lone Layer in Composition>

The multilayer structure layer (the first unit layer and the second unitlayer) and the lone layer had their compositions determined in theabove-described method by analyzing crystal grains in each layerappearing in a sample in the above-described cross section with an EDXdevice accompanying a TEM (JED-2300 (trade name) manufactured by JEOLLtd.). A result is shown in Tables 6-1 and 6-2.

<Analyzing Crystal Form of Multilayer Structure Layer and Lone Layer>

The multilayer structure layer (the first unit layer and the second unitlayer) and the lone layer had their crystal forms determined byanalyzing a pattern of a diffraction peak obtained through x-raydiffraction in the above described method. This was done using an X-raydiffractometer “MiniFlex600” (trade name) manufactured by RigakuCorporation. The X-ray diffractometer was used under the followingconditions. Tables 6-1 and 6-2 show a proportion (h/(c+h)) of hexagonalcrystal grains contained with reference to a total amount of cubiccrystal grains (c) and hexagonal crystal grains (h), as determined ineach layer.

Characteristic X-ray: Cu—Kα (wavelength: 1.54 angstrom)

Tube voltage: 45 kV

Tube current: 40 mA

Filter: Multi-layer mirror

Optical system: Focusing method

X-ray diffractometry: θ-2θ method

<Thickness of Multilayer Structure Layer and Lone Layer>

The multilayer structure layer (the first unit layer and the second unitlayer) and the lone layer were determined in thickness in the followingprocedure: Initially, each layer was determined in thickness bymeasuring each layer at any 10 points selected, as desired, in a samplein a cross section parallel to the direction of a normal to a surface ofthe substrate with a scanning transmission electron microscope (STEM)(manufactured by JEOL Ltd., trade name: JEM-2100F), and calculating anaverage value in thickness of the measured 10 points.

When the multilayer structure layer included two or more first unitlayers, then, initially, the above method was used to determine anaverage value in thickness of each first unit layer and an average valueof the determined values was defined as an average value in thickness ofthe first unit layers in the multilayer structure layer. When themultilayer structure layer included more than 10 first unit layers, thenin the first unit layers at 10 locations selected as desired, the abovemethod was used to determine an average value in thickness of a firstunit layer at each of the 10 locations and an average value of suchdetermined values was defined as an average value in thickness of themore than 10 first unit layers in the multilayer structure layer.Further, as the coating layer includes two or more multilayer structurelayers, average values in thicknesses of the first unit layers obtainedfrom the multilayer structure layers were further averaged to obtain anaverage value in thicknesses of the first unit layers. When the coatinglayer included more than 10 multilayer structure layers, any 10multilayer structure layers were selected and the above method was usedto determine an average value in thickness of first unit layers in eachof the 10 multilayer structure layers, and an average value of suchaverage values determined from the 10 multilayer structure layers wasdefined as an average value in thickness of the first unit layers. Thesecond unit layer's average value in thickness was also determined in asimilar manner.

The coating layer includes two or more lone layers. Accordingly, averagevalues in thickness determined from the lone layers were furtheraveraged to obtain a value, which served as an average value inthicknesses of the lone layers. A result is shown in Tables 6-1 and 6-2.

<Average, Maximum and Minimum Values in Thickness of Repetitive Unit>

The repetitive unit composed of one multilayer structure layer and onelone layer (hereinafter referred to as a “repetitive unit”) had averagevalue, maximum and minimum values in thickness, as determined in thefollowing method: In doing so, each repetitive unit was identified byhaving the lone layer deposited followed by the multilayer structurelayer, as seen at the substrate.

The repetitive unit's average value in thickness was determined by a sumof an average value in thickness of the multilayer structure layer andan average value in thickness of the lone layer. When the coating layerincluded more than 10 repetitive units, 10 successive repetitive unitswere selected in the coating layer, and an average value of the selected10 repetitive units was defined as an average value in thickness of themore than 10 repetitive units. In doing so, the 10 layers were selectedsuch that the interface between the fourth layer and the fifth layer inthe selected 10 layers was closest to the center of the coating layer.The coating layer's average value in thickness was divided by therepetitive unit's average value in thickness to calculate the number ofrepetitive units.

In determining the repetitive unit's maximum value in thickness,initially, a method similar to that described above was used todetermine a thickness of each repetitive unit in a sample in theabove-described cross section with a STEM. Subsequently, the repetitiveunit's determined value in thickness was compared with others' and amaximum value thereof was defined as a maximum value in thickness of therepetitive units. When the coating layer included more than 10repetitive units, 10 successive repetitive units were selected in thecoating layer, and a maximum value in the selected 10 repetitive unitswas defined as a maximum value in thickness of the more than 10repetitive units. In doing so, the 10 layers were selected such that theinterface between the fourth layer and the fifth layer in the selected10 layers was closest to the center of the coating layer. In doing so, anumerical value which seemed to be an apparently unexpected value wasexcluded. In a similar manner, the repetitive unit's minimum value inthickness was also determined. A result is shown in Table 9. In table 9,an indication “-” means that there is no corresponding parameter.

TABLE 9 lone layer repetitive unit average value average value maximumvalue minimum value ID in thickness in thickness in thickness inthickness symbol (nm) (nm) (nm) (nm)  [1] 8.1 27.5 40.6 12.6  [2] 3.243.9 57.7 28.0  [3] 8.4 39.2 52.8 12.9  [4] 2.6 43.7 57.5 23.8  [5] 4.846.5 55.3 12.6  [6] 4.9 48.6 57.5 14.8  [7] 8.7 50.0 59.0 16.3  [8] 4.448.4 57.3 29.6  [9] 9.2 46.2 55.0 12.2 [10] 8.5 29.6 42.8 10.4 [11] 8.132.3 45.6 17.5 [12] 7.2 18.1 39.8 8.4 [13] 16.3 68.7 73.7 36.3 [14] 6.715.9 38.5 9.8 [15] 13.9 59.2 63.6 31.0 [16] 5.9 32.1 45.4 17.7 [17] 5.634.9 48.3 15.3 [18] — — — — [19] 5000 — — —  [20]* — — — — *depositedthrough known PVD.

<<Cutting Test>>

(Cutting Evaluation: Continuous Processing Test)

Using the cutting tools of the thus prepared samples (sample nos. 1-1 to1-3 and 2 to 20) under the cutting conditions indicated below, a cuttingdistance (m) reached when the flank face was worn by an amount of 0.25mm or the cutting edge portion was broken was measured. Moreover, howthe cutting tools were damaged after cutting (i.e., a final damagedstate) was observed. A result thereof is shown in table 10. A cuttingtool providing a longer cutting distance can be assessed as a cuttingtool excellent in thermal cracking resistance and wear resistance.Furthermore, it is believed that a cutting edge portion easily attainshigh temperature under the cutting conditions indicated below.Accordingly, when a cutting tool is not observed to have breakage in adamaged state after cutting, the cutting tool can be assessed as acutting tool excellent in thermal cracking resistance.

Conditions for continuous processing test

Workpiece: FCD600 (a block material, W300×L50)

Cutter diameter: φ100

Cutting speed: 200 m/min.

Feed rate: 0.3 mm/t

Cutting Amount: 2 mm

Cutting width: 80 mm

Cutting oil: Wet type

TABLE 10 sample nos. cutting distance (m) final damaged state 1-1 6.3normally worn 1-2 6.9 normally worn 1-3 5.4 normally worn 2 6.6 normallyworn 3 6.3 normally worn 4 6.9 normally worn 5 7.5 normally worn 6 6.9normally worn 7 6.3 normally worn 8 6.3 normally worn 9 6 normally worn10 2.4 abnormally worn 11 2.4 abnormally worn 12 3 abnormally worn 132.1 abnormally worn 14 2.1 abnormally worn 15 2.4 abnormally worn 16 2.7abnormally worn 17 3 abnormally worn 18 2.4 abnormally worn 19 2.4abnormally worn 20 2.1 abnormally worn

As can be seen in Table 10, the cutting tools of sample Nos. 1-1 to 1-3and 2 to 9 (that is, the cutting tools of examples) provided a goodresult of a cutting distance of 5.4 m or more in continuous processing.The cutting tools of Sample Nos. 1-1 to 1-3 and 2 to 9 had their cuttingedge portions unbroken and normally worn (normally worn). In contrast,the cutting tools of sample Nos. 10 to 20 (the cutting tools of thecomparative examples) provided a cutting distance of 3 m or less incontinuous processing. The cutting tools of Sample Nos. 10 to 20 had afinal damaged state of being abnormally worn. Being “abnormally worn”includes being abnormally increasingly worn and being increasingly wornstarting from chipping or breakage. From the above results, it has beenfound that the cutting tools of the examples are excellent in thermalcracking resistance and wear resistance.

Thus while embodiments and examples of the present invention have beendescribed, it is also initially planned to combine configurations of theembodiments and examples, as appropriate.

It should be understood that the embodiments and examples disclosedherein have been described for the purpose of illustration only and in anon-restrictive manner in any respect. The scope of the presentinvention is defined by the terms of the claims, rather than theembodiments and examples described above, and is intended to include anymodifications within the meaning and scope equivalent to the terms ofthe claims.

REFERENCE SIGNS LIST

-   -   1 rake face, 2 flank face, 3 cutting edge ridge portion, 10        substrate, 11 multilayer structure layer, 11 a first unit layer,        11 b second unit layer, 12 lone layer, 13 underlying layer, 14        surface layer, 20 coating layer, 30 coating, 50 CVD apparatus,        52 substrate setting jig, 53 reaction container, 54 temperature        controller, 55 first gas introduction pipe, 56 second gas        introduction pipe, 57 third gas introduction pipe, 58 gas        introduction pipe, 59 gas exhaust pipe, 60 gas exhaust port, 100        cutting tool

The invention claimed is:
 1. A cutting tool comprising a substrate and acoating layer provided on the substrate, the coating layer including amultilayer structure layer composed of a first unit layer and a secondunit layer, and a lone layer, the first unit layer and the second unitlayer being alternately stacked, the multilayer structure layer and thelone layer being stacked such that more than one multilayer structurelayer and more than one lone layer are alternately stacked, the firstunit layer including cubic Al_(x)Ti_(1-x)N crystal grains, the secondunit layer including cubic Al_(y)Ti_(1-y)N crystal grains, the lonelayer including cubic Ti_(z)Al_(1-z)N crystal grains, an atomic ratio xof Al in the Al_(x)Ti_(1-x)N being 0.8 or more and 0.95 or less, anatomic ratio y of Al in the Al_(y)Ti_(1-y)N being 0.7 or more and lessthan 0.8, an atomic ratio z of Ti in the Ti_(z)Al_(1-z)N being 0.55 ormore and 0.7 or less, the first unit layer having a thickness with anaverage value of 2.5 nm or more and 5 nm or less, the second unit layerhaving a thickness with an average value of 2.5 nm or more and 5 nm orless, the multilayer structure layer having a thickness with an averagevalue of 10 nm or more and 45 nm or less, the lone layer having athickness with an average value of 2.5 nm or more and 10 nm or less, onemultilayer structure layer and one lone layer forming a repetitive unithaving a thickness with an average value of 20 nm or more and 50 nm orless, a maximum value of 40 nm or more and 60 nm or less, and a minimumvalue of 10 nm or more and 30 nm or less.
 2. The cutting tool accordingto claim 1, wherein the lone layer has a thickness with an average valueof 2.5 nm or more and 5 nm or less.
 3. The cutting tool according toclaim 1, wherein the repetitive unit has a thickness with an averagevalue of 25 nm or more and 50 nm or less, a maximum value of 50 nm ormore and 60 nm or less, and a minimum value of 12 nm or more and 30 nmor less.
 4. The cutting tool according to claim 1, wherein the coatinglayer has a thickness with an average value of 0.1 μm or more and 10 μmor less.
 5. The cutting tool according to claim 1, further comprising anunderlying layer provided between the substrate and the coating layer,wherein the underlying layer is composed of a compound consisting of: atleast one element selected from the group consisting of a group 4element, a group 5 element and a group 6 element of the periodic tableand aluminum; and at least one element selected from the groupconsisting of carbon, nitrogen, oxygen and boron, and the underlyinglayer is different in composition from the first unit layer, the secondunit layer, and the lone layer.
 6. The cutting tool according to claim1, further comprising a surface layer provided on the coating layer,wherein the surface layer is composed of a compound consisting of atleast one element selected from the group consisting of: a group 4element, a group 5 element and a group 6 element of the periodic tableand aluminum; and at least one element selected from the groupconsisting of carbon, nitrogen, oxygen and boron, and the surface layeris different in composition from the first unit layer, the second unitlayer, and the lone layer.